Hi everybody!
Do you have any experience with how much resources is needed to run a server for several dozen thousand participants and up to a few hundred/thousand users filling in the survey simultaneously?

A useful hint about setting memory size has been added to instructions recently (docs.limesurvey.org/General+FAQ#Fatal_er..._Allowed_memory_size). Is it enough to avoid performance issues with bigger surveys? Are there other server parameters (apart from basic requirements listed at the beginning of the limesurvey manual) that should be taken into consideration?

1. The survey size and how many questions are presented on a single page.

2. The (extensive) use of conditions. There have been some remarkable improvements at Limesurvey 1.92 so consider updating if this might cause trouble.

3. The number of users per hour/minute/second.

In general for large surveys with lots of users you should never use a shared hosting but use your own server. Depending on the number of users the server should provide at least a dual core CPU and 2GB RAM. Hard disk isn't that important.

Thank you for your answer!
Is it possible to give some general equations to each of those variables (survey size, questions/page, conditions, users), which would allow to roughly calculate, what specific resources are needed in case of a given survey?

Thank you for your answer!
Is it possible to give some general equations to each of those variables (survey size, questions/page, conditions, users), which would allow to roughly calculate, what specific resources are needed in case of a given survey?

Sorry, that isn't possible because there are two many variables and too many unknown values such as number of users/minute at peak times and the like.

Here are estimated peak-time values for 5 surveys, each of them having similiar parameters, as stated in the post before, ALTOGETHER (all 5 surveys' users summed up):
- max 750 users/day
- max 75 users/hour
- max 30 users/minute (the average time of filling the questionnaire is 20 min and in the peak time every minute someone starts to fill it)
Could you just very roughly estimate the resources needed? It would be extremeley helpful for preparing some apropriate server for the survey!

I think you could start with a dual core server with 2-4GB RAM. If these are really important surveys I recommend to use www.LimeService.com which is a Limesurvey optimized hosting with a server cluster that has never even touched ressource limits ever.

User have dealt with 20.000 participants/day without problems.
I think you could start with a dual core server with 2-4GB RAM. If these are really important surveys I recommend to use www.LimeService.com which is a Limesurvey optimized hosting with a server cluster that has never even touched ressource limits ever.

1.) What kind of clustering is used on limeservice.com?

2.) Performance and Resources: While monitoring a few test installations I stumbled across the creation of session files by limesurvey. A survey with 138 questions / 72 groups (half of them created for mimic looping) is creating a 2-2,5MB session file when hitting the welcome page. That behaviour occured on 1.92+ and the lastest 2.X of Limesurvey.

On many servers the tmp is mounted separately with a limited size.
So the session files are filling the tmp space up quickly.

Would be interesting to know, what's the typical session file size on other projects.